OBJECTIVE To determine the behavioral and hormonal interactions between mothers and daughters and the flexibility of group transfers for young females. To establish fecal steroid analysis for monitoring wild marmosets. RESULTS We studied seven mother-daughter behavioral and hormonal interactions in undisturbed family groups. We performed 30-minute focal animal behavioral observations three times per week and collected fecal samples at least twice a week for behavioral monitoring of reproductive and adrenal steroids for two months. In contrast to daughter tamarins that show no signs of ovulatory cycles in the family, five of the seven daughter marmosets (71%) showed ovarian cycling. For four of these daughters, the mother was pregnant during the sampling period and the other female had a mother who showed ovarian cycling. Two daughters showed no signs of ovarian cycling while one had a cycling mother and the other did not. Cortisol levels were higher in daughtersQcycling or noncyclingQthan in mothers. Early pregnancy was associated with the lowest levels of cortisol. Preliminary analysis of behavioral data indicated that social interactions between mothers and daughters were elevated when daughters w ere cycling. The two females that were not showing ovarian cycling exhibited a higher frequency of play behaviors than the cycling females. Eldest daughters were then removed from the family and paired with an unfamiliar male in another part of the colony. After two months of behavioral and endocrine data collection, the daughter marmosets were then replaced back with their families for two months and behavioral and endocrine data collected. Upon pairing with unfamiliar males, cortisol levels increased significantly during the first 20 days. All but one female showed ovarian steroid cyclicity during the paired staged. All females exhibited reproductive behavior towards their male and one female became pregnant. When females were brought back to their natal families, the mothers showed no overt aggression in all 7 returns except for one mother. Only daughters with younger female siblings in the family were prevented from entering the group. There were also insignificant changes in corti sol when returning to the natal group. Of the six that were cycling when they returned, only one female stopped cycling. While data analysis is still underway, it is apparent that social transitions are associated with elevated cortisol levels as occurs with cotton-top tamarins. Furthermore, daughters leaving the family group to interact with males do appear able to rejoin groups without being reproductively suppressed. FUTURE DIRECTIONS Fecal samples will be analyzed for steroids KEY WORDS fecal steroids, adrenal response, social transitions, ovarian cycling, socioendocrinology FUNDING NIMH MH56413-01 PUBLICATIONS Sousa M.B., and T.E. Ziegler. 1998. Diurnal variation on the excretion patterns of fecal steroids in common marmoset (Callithrix jacchus) females. Am J. of Primatology 46:105-117.